Cancer is associated with venous thromboembolism in 20% of patients. In such patients, thrombosis is difficult to treat, associated with bleeding, recurrence, and death. Specific treatments for venous thromboembolism in cancer are recommended. Guidelines have been implemented in many countries and international guidelines have been recently developed. We evaluated the adhesion to national French guidelines via a survey of cancer patients treated for venous thromboembolism. METHODS: A national cross-sectional observational study evaluated the adhesion to guidelines in hospitalized patients. Good clinical practice was defined as initial 10-day treatment with injectable molecules followed by long-term treatment with low molecular weight heparin for at least 3 months. Demographic data, cancer type, stage, treatment, risk factors and type of thrombosis, were recorded. RESULTS: Five patients were included in 47 centers. Overall adhesion to guidelines was present in 59% (55-63%) of patients (295/500). During initial treatment, adhesion was high (487/496; 98%) but dropped (296/486; 62%) during the long-term maintenance. In patients with renal insufficiency, only a fourth of them received the adequate treatment. A majority of patients had metastatic disease (64%). Cancer sites were gastro-intestinal (25%), gynecologic (23%), pulmonary (21%), hematological (14%), urologic (10%), or other (8%). Lung and hematological malignancies were significantly associated with the highest and lowest rates of adhesion. CONCLUSION: Adhesion to national guidelines for treatment of venous thromboembolism in cancer is not optimal. Good compliance is observed during initial treatment, but drops after 10 days, underlying the need for further education to achieve a better implementation on a national level.